An ad-hoc network is a kind of a self-configuring network linked through radio communication. The ad-hoc network is made up of multiple nodes. The nodes in the ad-hoc network transmit and receive packets through multi-hop communication. Multi-hop communication is a technique enabling nodes that not present in one another's communication area to communicate, via other nodes present in the communication areas of the nodes.
If an ad-hoc network is connected to another network such as the Internet, a local area network (LAN), and a wide area network (WAN), a relay device called gateway is used to transfer communication between networks.
Technology utilizing an ad-hoc network includes a system that incorporates a node capable of radio communication with an electricity meter at a household to perform operations such as checking the meter through the ad-hoc network without actually going to the site. An ad-hoc network handling personal information such as electricity usage of each household is required to perform secure communication with respect to confidentiality and tampering prevention.
Therefore, conventional systems encrypt packets transmitted and received between nodes in an ad-hoc network to ensure secure communication. In this case, use of an encryption key common to all the nodes in the system poses a greater risk if the key is compromised and therefore, some systems change the encryption key for each gateway.
At the time of initial introduction, etc. of a new node into a system, the new node cannot perform secure communication with other nodes in an ad-hoc network until an encryption key is set. Therefore, it is difficult to automatically set an encryption key for the new node through the ad-hoc network and an operator has to actually go to the site to set an encryption key.
Prior arts related to secure communication include, for example, a technique of managing an encryption key of a network in which communication is performed by broadcasting (see, e.g., Japanese Laid-Open Patent Publication No. 2003-348072); a technique for stably executing key exchange at the start of communication in an ad-hoc network (see, e.g., Japanese Laid-Open Patent Publication No. 2007-88799); and a technique for allowing each node in an ad-hoc network to select an adaptive gateway (see, e.g., Japanese Laid-Open Patent Publication No. 2009-81854).
However, if the encryption key set for nodes in an ad-hoc network is changed for each gateway, the conventional techniques have a problem in that it is difficult to identify the gateway to which a new node belongs at the time of initial introduction, etc. of the new node. For example, even if a candidate gateway can be narrowed down by the address of the location of a new node, the communication status changes due to factors such as weather and a positional relationship with nearby buildings. Therefore, an operator must actually go on-site to confirm which gateway is communicable, arising in a problem in that the work hours of the operator and the workload required for setting the encryption key increase.